Manny Pacquiao is shown working a speed bag. He fights Timothy Bradley on Saturday. There last fight was a controversial finish that awarded the win to Bradley.(Photo: Jayne Kamin-Oncea USA TODAY Sports)

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LAS VEGAS -- Joel Diaz wasted no time answering the question put before him Wednesday: Do the trainer and his fighter, Timothy Bradley, believe they will send Manny Pacquiao into retirement Saturday night when they meet in their much-anticipated rematch?

"That's what we're here for," said Diaz, who has been waiting for this moment since Bradley was judged the controversial split-decision winner against Pacquiao in their first fight on June 9, 2012, and saw their lives unravel in a constant stream of criticism over the decision. "I think it's Manny Pacquiao's last fight. Like everything in life, everything has a beginning and an end.

"I think this is Manny Pacquiao's end."

That thought has been on peoples' minds since Pacquiao was knocked out by Juan Manuel Marquez in December 2012. Even Pacquiao's longtime trainer, friend and confidant, Freddie Roach, has faced the inevitable question. His bond with Pacquiao is tight enough that he will tell the Filipino when it's time.

That bond could be tested Saturday when Pacquiao (55-5-2, 38 KOs) takes on WBO welterweight champion Bradley (31-0, 12 KOs) at the MGM Grand Garden Arena (HBO pay-per-view, 9 p.m. ET) in the followup to a decision so controversial it launched a WBO investigation. Pacquiao won in the court of public opinion but not on the scorecards.

Pacquiao, a second-term congressman in the Philippines, took nearly a year off before returning in Macau in November, where he defeated a much younger Brandon Rios by unanimous decision.

But Rios is not Bradley.

For Pacquiao it's make-or-break time against a fighter who has never lost. Furthermore, Bradley is coming off two impressive victories: the 2013 fight of the year against Ruslan Provodnikov, who is trained by Roach, and a unanimous decision against Marquez.

Roach considers this a "must-win" fight and says if Pacquiao, 35, loses a second time to Bradley and he notices slippage, he will tell his friend to quit.

He doesn't anticipate having to have that talk, though, because he thinks Pacquiao will has what it takes to become a champion again.

"He's still the hardest worker in the gym," Roach says. "He still gives me everything I want, and his dedication is still 100 percent there. He's still the most disciplined fighter I've ever had."

Yet, Diaz senses that Pacquiao's career has come down to one fight at a time.

"I'm a trainer, and I've trained fighters in their prime and I've trained fighters toward the end of their prime," Diaz said. "Common sense says Manny Pacquiao, at his age, has a lot of wear and tear on his body. I don't remember when the last time he had a knockout.

"And then his lifestyle changed to the point where he's now compassionate to his opponents. If you're compassionate to your opponents, you don't belong in this sport. Find another sport. Go play golf or tennis."

Promoter Bob Arum says the idea this could be an aging boxer's last fight is nothing new: "As a guy puts on years, there's always talk that if he does poorly, this could be his last fight. For example, if he should get beat up in this fight, those of us who really care for him would counsel him to hang up the gloves.

"He's been fighting since he's 15. So any fight at this time for a fighter with that resume could be his last fight. But that doesn't mean we're anticipating that this will be his last fight."

A Pacquiao victory, says Roach, is all but a must.

"Since we lost – and it was a (bad decision) but we still lost — we're the ones who have to win and take that off the record," Roach said, "because in the history of boxing, you have to avenge those losses, and in the books, we lost that fight."

While we thought it was a bad decision, you have to live with it. We lost the fight and we have to get it back."

Bradley, 30, questions Pacquiao's killer instinct. He points to the fact that Pacquiao, who has had some spectacular knockouts during his 19-year pro career, has not had one since flattening Ricky Hatton in 2009. Like Diaz, Bradley believes Pacquiao's religious beliefs have sapped him of the will to put a fighter away. Pacquiao's response?

Roach had a long talk with Pacquiao, who quit gambling, drinking and womanizing and began to become almost obsessed by the Bible shortly before the first Bradley fight.

"I said, 'Manny, if you don't knock them out when you have the opportunity, then one punch can change a fight as we found out with Marquez, you know? You need to get guys out of there if you hurt them, and I think he realizes that's a true statement.

"He has to have that drive he once had. He's holding back because he may be into the Bible a little too much. I told him there's lot of violence in the Bible and there's lots of payback in the Bible, and there's a lot of killer instinct in the Bible. And he had to agree with me."

"I think that talk, and Bradley telling him he lost the killer instinct helped quite a bit also. It was like a slap in the face to Manny. I think he has it and I think he'll show it."

And if he doesn't, and is beaten decisively on Saturday?

"If that happens, we will have that discussion, yes," Roach said. "We're pretty close, and he's asked me, 'when I'm all done, will you tell me?' I said of course I will. And I said, 'will you quit?' and he said 'of course I will.' We're in agreement there."

Pacquiao, says Roach, is not fighting for the money or for any other reason than "he still loves the sport and he knows what he does best. He has a career in politics if he wants to quit fighting, and that's already there. And it's something that can get bigger and bigger and bigger if he wants. But right now he chooses to do what he does best."

Meanwhile, Jinkee, who is expecting their fifth child later this month, a boy they will name Israel, has reconciled her belief that he should retire. Of course, another $20 million or more payday for her husband, still one of the sport's most popular pay-per-view stars, doesn't hurt either.

"She's OK with (me fighting)," Pacquiao said. "I told her that if I feel something in my body I will tell her and I will not keep on fighting. But right now, you know, I thank God, He gave me good health and spirit every day and I feel good."

Pacquiao also says hearing retirement talk is "not new for me. I heard that in my last fight with Rios. He said I would have to retire after the fight. But you have to prove it in the ring."

Pacquiao say he could fight for a couple more years if things go as planned.

"And that's it. I don't want to retire and come back later," he said. "When I retire, there's no coming back."